Mineral fiber products, particularly products made of glass fibers, are typically made as either continuous fibers or discontinuous fibers. Various organic coatings are applied to these fibers for protecting the fibers from abrasion, for connecting the mineral fibers to each other to form a structural product, and for providing compatibility of the mineral fibers with other materials, such as the compatibility between reinforcement fibers and a plastic matrix. In the case of insulation products, the mineral fibers are bonded together by organic material, such as a phenol/formaldehyde binder, to form a spring-like matrix which can recover after compression during packaging.
The application of organic material to the mineral fibers can take several forms. Continuous mineral fibers can be run through a bath or across a coater to apply a coating to the fibers, such as during the application of a size to continuous fibers. Also, the organic material can be sprayed onto the mineral fibers. This method is commonly used in the manufacture of insulation products where downwardly moving a cylindrical veil of mineral fibers is met with the sprays of the phenol/formaldehyde binder. Typically, the phenol/formaldehyde binder contains urea, and has a molecular weight of around 600 in the uncured state in the aqueous solution being applied to the glass fibers.
One of the problems with applying aqueous organic binders of the prior art to cylindrical veils of mineral fibers is that a portion of the binder tends to evaporate prior to contact between the liquid binder drop and a mineral fiber in the veil. The evaporated binder material becomes a contaminant in the exhaust air stream of the process and must be cleaned up in order to avoid pollution problems. Also, the binder material on the mineral fibers tends to be sticky, requiring extensive cleaning of the fiber collection apparatus to prevent the build-up of clumps of glass fiber insulation material which can drop into the product and cause a product defect.
Another problem associated with the application of binder to insulation products is that the low molecular weight phenol/formaldehyde binder material does not have some of the desirable characteristics of other, higher molecular weight polymeric material, such as polyethylene terephthalate (PET), polypropylene, or polyphenylene sulfide (PPS). A primary problem with the low molecular weight binder material is that a curing process is required, and this usually has operating penalties such as the capital and operating cost of a curing oven, the cost of handling pollution problems, degree of cure problems and product integrity problems. If higher molecular weight polymers could be applied to mineral fibers to produce insulation products, some improved features and efficiencies could be realized.
A method recently developed for applying higher molecular weight binders to mineral fibers to produce an insulation product includes the use of two coaxial rotary spinners, an upper spinner for fiberizing glass fibers from molten glass, and a coaxial lower spinner for fiberizing organic material. The glass fibers are directed into a downwardly moving cylindrical veil, and the spinner for the organic fibers is positioned within the veil. The organic fibers are directed radially into contact with the glass fibers, where some of the organic fibers melt and form a coating or binder on the glass fibers. Some of the organic fibers retain their fibrous form. The resulting product exhibits excellent molding properties for insulation and structural glass fiber products. The above-described cofiberizing technology is the subject of U.S. Pat. Nos. 5,458,822 and 5,490,961, both of which are assigned to the assignee of the present invention, and both of which are hereby incorporated by reference.
A problem with the above-described cofiberizing process is that the use of coaxial spinners dictates narrow operating windows on both the glass fiberizing process and the organic fiberizing process. The temperature of the environment surrounding the glass fiber spinner must be tailored to accommodate the temperature limitations of the organic material. Degradation of the organic material is more pronounced at higher percentages of organic material than when only low percentages of organic material is used. It would be advantageous to have a process for integrating organic material, in either fibrous or non-fibrous form, into a veil or stream of mineral fibers without requiring the use of coaxial spinners.